This invention relates generally to gas-insulated transmission lines and more particularly to a gas-insulated transmission line utilizing means for limiting the DC voltage on the inner conductor on the line.
Compressed gas-insulated transmission lines are being used in an ever increasing scale in recent years due to the desirability of increasing safety, problems in acquiring right-of-way for overhead lines, and higher power loads required by growing metropolitan areas and growing demands for electrical energy. Gas-insulated transmission lines typically comprise a hollow sheath, a conductor disposed within the sheath, a plurality of solid insulating spacers which support the conductor, and a compressed gas such as sulfur hexafluoride or the like in the sheath to electrically insulate the conductor from the sheath. The typical assembly has been fabricated from relatively short sections of hollow cylindrical ducts or tubes in which the conductor and insulators are inserted. This assembly is usually completed in the factory, and the sections are welded or otherwise secured together in the field to form the transmission line. Gas barriers are provided at intervals along the length of the assembly, and, after evacuation on the line, an insulating gas is forced into the the sheath under pressure. It is also known to provide a particle trap in compressed gas insulated transmission lines as is disclosed in the patent to Trump, U.S. Pat. No. 3,515,939.
The majority of the gas-insulated transmission lines installed to date have been utilized for the transport of alternating current, or AC, voltages. As such, they have been designed to withstand these AC voltages. However, under certain circumstances there is the possibility that DC voltages may be present on the inner conductor. For example, if breakers or switches are opened at either end of an unloaded line, such opening of the line will cause a DC voltage to become trapped on the line. As the transmission line has not been designed for DC voltages, there is an increased probability that the line will sustain serious damage due to the effects of the DC trapped charge.